Display devices have utilized a variety of techniques to provide dynamic or static images. According to one type of display, an array of pixels emit colored light to achieve an image discernable by an operator. Such emissive displays can utilize pixels comprised of organic light emitting diode (OLED) and polymer light emitting diode (PLED) elements. For a conventional color display, each color pixel is comprised of at least three OLED or PLED elements.
With reference to FIG. 1, a conventional pixel 20 for a conventional display includes a red element 22, a blue element 24 and a green element 26. As shown in FIG. 1, elements 22, 24, and 26 have essentially the same area with respect to each other. Elements 22, 24, and 26 can be patterned according to various photolithographic pattern technologies. Elements 22, 24, or 26 can be PLED or OLED elements or other emissive elements. U.S. Pat. No. 6,013,538, U.S. Pat. No. 6,013,982 and U.S. Pat. No. 6,023,259 describe OLED elements.
According to conventional systems, element 22 emits a first particular color, element 24 emits a second particular color and element 26 emits a third particular color. Elements 22, 24, and 26 each contain unique materials with respect to each other so that they emit the first, second or third color, respectively, in response to a drive signal. However, certain materials emit brighter or higher luminance light than materials associated with other colors in response to the same drive signal. Accordingly, prior art systems have driven weaker color elements at higher voltages relative to the others to provide the appropriate luminance and chromaticity for pixel 20.
Driving weaker elements harder than others accelerates the degradation of those weaker color elements. For example, if element 22 is driven harder than element 26, element 22 will degrade and eventually fail before element 26. Therefore, the need to drive one of elements 22, 24, and 26 with more energy than other elements leads to a premature failure of the display.
Thus, there is a need for an emissive display having pixels comprised of elements which are driven equally. Further still, there is a need for a display which addresses efficiency, luminance, chromaticity and lifetime. Even further still, there is a need for a pixel having OLED or PLED elements optimized for operation in a most efficient operating region.